The present invention relates to a novel polysaccharide which is produced by a marine bacterium.
The bacterial subspecies Alteromonas macleodii subsp. fijiensis was isolated from submarine hydrothermal springs. When it is cultured under laboratory conditions on a glucose-rich medium, this bacterium secretes large quantities of exopolysaccharides. The morphological, physiological and phylogenetic characteristics of Alteromonas macleodii subsp. fijiensis are reported in the publication by RAGUENES et al., [Applied and Environmental Microbiology, 62(1), pp. 67-73, (1996)].
This publication also provides information on the overall composition of the polysaccharide mixture, which is produced by an Alteromonas macleodii subsp. fijiensis strain designated ST716 and cultured on glucose-enriched medium, and which is recovered from this medium by precipitating with ethanol.
This polysaccharide mixture comprises (percentages by weight) 10.5% of glucose, 11.1% of galactose, 4.4% of mannose, 5% of pyruvate-substituted mannose, 12.2% of glucuronic acid and 6.3% of galacturonic acid, corresponding to respective molar ratios of glucose, galactose, mannose, glucuronic acid and galacturonic acid of 1.0/1.1/0.6/1.1/0.6. Its content of sulfates is 5%.
The inventors have sought to identify the constituents of this mixture and have purified a novel polysaccharide from it.
This purified polysaccharide, which is the subject-matter of the present invention, is composed of glucose, galactose, glucuronic acid, galacturonic acid and pyruvate-substituted mannose.
It is characterized in that these different constituents are respectively present in the molar ratios of 1/1/1/2/1 and are combined in one repetitive hexasaccharide unit in which three glycosidic residues form a main chain whose branching point consists of a galacturonic acid residue. A side chain, which is terminated by a mannose residue which is substituted by pyruvate in position 4 and position 6, is grafted onto this latter galacturonic acid residue.
A polysaccharide in accordance with the invention consists of n hexasaccharide units (n being equal to or greater than 1), corresponding to the formula (I) below: 
A polysaccharide according to the invention can, for example, be purified from the exopolysaccharides which are produced by the ST716 strain. On Oct. 17, 1995, this strain was deposited by IFREMER, in accordance with the Budapest Treaty, in the CNCM (Collection Nationale de Cultures de Microorganismes [National Collection of Microorganism Cultures]), which is held by the Pasteur Institute, 25 rue du Docteur Roux, Paris, under the number I-1627.
According to a preferred embodiment of the present invention, a polysaccharide of formula (I), which has been purified by anion exchange chromatography from the exopolysaccharide mixture secreted by Alteromonas macleodii subsp. Fijiensis, possesses an average molecular weight (Mw) of the order of 106 Da, that is an average degree of polymerization, DPn, of the order of 800.
The composition of the polysaccharide according to the invention, and its highly branched structure, confer on it the following rheological characteristics:
it possesses, for an average molecular weight (Mw) of the order of 106 Da, an intrinsic viscosity, xcex7, of the order of 2 600 ml.gxe2x88x921,
its viscosity increases in the presence of Ca2+ ions but it remains stable in the presence of Mg2+ and K+ ions;
it possesses a thickening power and a rheofluidifying behavior; these thickening properties are stable at a pH of between 4.5 and 9.
The invention therefore also relates to the use of a polysaccharide according to the invention as a thickening agent and as a rheofluidifying agent.
These rheological characteristics, combined with its hydrophilicity and its solubility, make the polysaccharide according to the invention of considerable interest for use in a variety of industries, in particular in the farm-produce industry, as a texturizing, stabilizing and/or thickening agent.
For this reason, the invention also relates to the use of a polysaccharide according to the invention as a texturizing, in particular stabilizing and/or thickening, agent in the farm-produce industry.
The invention more specifically relates to the use of a polysaccharide according to the invention for preparing a product which is intended for feeding to humans or animals.
The polysaccharides according to the invention can, for example, be used for conferring the desired consistency on liquid, creamy, pasty, gelatinous or semisolid products, while at the same time improving and/or stabilizing their texture.
In particular, the polysaccharides stabilize products which are subjected to substantial variations in temperature, for example during cooking or UHT treatment, or during freezing, when the polysaccharides prevent the formation of ice crystals.
The polysaccharides can also be used for retaining moisture in solid products, in order to impart a soft texture to these products and to ensure that this soft texture is preserved.
The polysaccharides according to the invention can be incorporated very readily and homogeneously into any preparations made in the presence of water. It is therefore very simple to use them in industrial processes and, in addition, they are particularly suitable for making xe2x80x9cready-to-usexe2x80x9d products for reconstitution by the final consumer.
The polysaccharides according to the invention can also be used for clarifying liquid products which are intended for use as foodstuffs, such as wines or vinegar.
The present invention also encompasses products which are intended for feeding to humans or animals and which comprise at least one polysaccharide according to the invention.
The polysaccharides according to the invention are advantageously present in the products in question in a proportion of from 0.01 to 10%, preferably of from 0.05 to 5%, by weight, based on the total weight of the ingredients.
The present invention will be understood more fully with the aid of the remainder of the description, which follows and which refers to nonlimiting examples which illustrate the purification and characterization of a polysaccharide according to the invention and its properties and uses.